Each ring sector comprises a circumferential flange at one end thereof, which is radially clamped on an annular rail of the casing through a substantially C-shaped cross-section resilient lock which is axially engaged on the casing rail and the circumferential flange of the ring sector.
The lock is formed with two circumferentially directed parallel walls, respectively inner and outer, which extend one inside the other and which are connected together by a substantially radial wall. The inner and outer walls of the lock comprise radial supporting or bearing means on the flange of the ring sector and the casing rail, respectively. The lock is engaged on the flange of the sector and on the casing rail with a radial preload. In the idle state of the turbomachine, the inner and outer walls of the lock radially bear on the flange of the ring sector and on the casing rail substantially all along the width or angular extent of the lock.
In the operating state, a temperature gradient relatively substantial in a radial direction appears in each ring sector, which causes a “discambering” of this ring sector. This phenomenon further translates into an increase of the curvature radius of the ring sector, which decreases the radial bearing surfaces between the walls of the lock and the flange of the ring sector and the casing rail. It has been noticed that the bearing areas between those pieces were essentially located between the end portions of the outer wall of the lock and the casing rail, and between the median portion of the inner wall of the lock and the ring sector. The stresses communicated by the ring sector and the casing rail pass in transit through those bearing areas which are not optimized and then form concentration areas for strains capable of reducing the lifetime of the lock.